Summary
Depolymerized holothurian glycosaminoglycan (DHG) is a glycosaminoglycan extracted
from the sea cucumber Stichopus japonicusSelenka. In previous studies, we demonstrated that DHG has antithrombotic and anticoagulant
activities that are distinguishable from those of heparin and dermatan sulfate. In
the present study, we examined the effect of DHG on the tissue factor pathway inhibitor
(TFPI), which inhibits the initial reaction of the tissue factor (TF)-mediated coagulation
pathway. We first examined the effect of DHG on factor Xa inhibition by TFPI and the
inhibition of TF-factor Vila by TFPI-factor Xa in in vitro experiments using human
purified proteins. DHG increased the rate of factor Xa inhibition by TFPI, which was
abolished either with a synthetic C-terminal peptide or with a synthetic K3 domain
peptide of TFPI. In contrast, DHG reduced the rate of TF-factor Vila inhibition by
TFPI-factor Xa. Therefore, the effect of DHG on in vitroactivity of TFPI appears to be contradictory. We then examined the effect of DHG on
TFPI in cynomolgus monkeys and compared it with that of unfractionated heparin. DHG
induced an increase in the circulating level of free-form TFPI in plasma about 20-fold
when administered i.v. at 1 mg/kg. The prothrombin time (PT) in monkey plasma after
DHG administration was longer than that estimated from the plasma concentrations of
DHG. Therefore, free-form TFPI released by DHG seems to play an additive role in the
anticoagulant mechanisms of DHG through the extrinsic pathway in vivo. From the results
shown in the present work and in previous studies, we conclude that DHG shows anticoagulant
activity at various stages of coagulation reactions, i.e., by inhibiting the initial
reaction of the extrinsic pathway, by inhibiting the intrinsic Xase, and by inhibiting
thrombin.
